Section: User Commands (1)
Updated: May 1996
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readprofile - a tool to read kernel profiling information
This manpage documents version 2.0 of the program.
command uses the
information to print ascii data on standard output.
The output is
organized in three columns: the first is the number of clock ticks,
the second is the name of the C function in the kernel where those many
ticks occurred, and the third is the normalized `load' of the procedure,
calculated as a ratio between the number of ticks and the length of
the procedure. The output is filled with blanks to ease readability.
Available command line options are the following:
- -m mapfile
Specify a mapfile, which by default is
You should specify the map file on cmdline if your current kernel isn't the
last one you compiled, or if you keep System.map elsewhere. If the name of
the map file ends with `.gz' it is decompressed on the fly.
- -p pro-file
Specify a different profiling buffer, which by default is
Using a different pro-file is useful if you want to `freeze' the
kernel profiling at some time and read it later. The
file can be copied using `cat' or `cp'. There is no more support for
compressed profile buffers, like in
because the program needs to know the size of the buffer in advance.
Info. This makes
only print the profiling step used by the kernel.
The profiling step is the resolution of the profiling buffer, and
is chosen during kernel configuration (through `make config'),
or in the kernel's command line.
(terse) switch is used together with
only the decimal number is printed.
Print all symbols in the mapfile. By default the procedures with 0 reported
ticks are not printed.
Print individual histogram-bin counts.
Reset the profiling buffer. This can only be invoked by root, because
is readable by everybody but writable only by the superuser. However,
you can make
setuid 0, in order to reset the buffer without gaining privileges.
- -M multiplier
On some architectures it is possible to alter the frequency at which
the kernel delivers profiling interrupts to each CPU. This option allows you to
set the frequency, as a multiplier of the system clock frequency, HZ.
This is supported on i386-SMP (2.2 and 2.4 kernel) and also on sparc-SMP
and sparc64-SMP (2.4 kernel). This option also resets the profiling buffer,
and requires superuser privileges.
Verbose. The output is organized in four columns and filled with blanks.
The first column is the RAM address of a kernel function, the second is
the name of the function, the third is the number of clock ticks and the
last is the normalized load.
Version. This makes
print its version number and exit.
Browse the profiling buffer ordering by clock ticks:
readprofile | sort -nr | less
Print the 20 most loaded procedures:
readprofile | sort -nr +2 | head -20
Print only filesystem profile:
readprofile | grep _ext2
Look at all the kernel information, with ram addresses"
readprofile -av | less
Browse a `freezed' profile buffer for a non current kernel:
readprofile -p ~/profile.freeze -m /zImage.map.gz
Request profiling at 2kHz per CPU, and reset the profiling buffer
sudo readprofile -M 20
only works with an 1.3.x or newer kernel,
changed in the step from 1.2 to 1.3
This program only works with ELF kernels. The change for a.out kernels
is trivial, and left as an exercise to the a.out user.
To enable profiling, the kernel must be rebooted, because no profiling module
is available, and it wouldn't be easy to build. To enable profiling,
you can specify "profile=2" (or another number) on the kernel commandline.
The number you specify is the two-exponent used as profiling step.
Profiling is disabled when interrupts are inhibited. This means that many
profiling ticks happen when interrupts are re-enabled. Watch out for
/proc/profile A binary snapshot of the profiling buffer.
/usr/src/linux/System.map The symbol table for the kernel.
/usr/src/linux/* The program being profiled :-)
The readprofile command is part of the util-linux-ng package and is available from
This document was created by
using the manual pages.